Processing liquids such as alcohols and glycols are used in the production of natural gas from oil and gas wells. Thus, typical processing liquids include alcohols and glycols such as mono-, di-, or tri-ethylene glycols (MEG, DEG, and TEG, respectively). When used in the production of natural gas, the processing liquids quickly become contaminated with water, e.g., produced water from the formation, as well as, alkaline metal cations such as magnesium, calcium, etc. and other contaminants primarily dissolved salts such as sodium chloride. Water-insoluble salts of the alkaline earth metal cations are a common cause of fouling in heat exchangers, reboilers, transfer lines, pumps, valves, etc. which are used in systems for recovering the processing liquid for reuse.
U.S. Pat. Nos. 5,152,887; 5,158,649; 5,389,208; 5,441,605; 5,993,608;and 6,508,916, all of which are incorporated herein by reference for all purposes, deal with the recovery or reclamation of processing fluids used in gas processing including the production of natural gas from oil and/or gas wells.
As noted above, processing liquids such as MEG used in natural gas production become contaminated with alkaline earth metal cations, primarily calcium and magnesium. Presently, to deal with these cations which can form substantially water-insoluble salts accompanied by the attendant problems described above, it is common to attempt to remove these cations prior to any regeneration and/or reclamation by effecting precipitation of the cations using precipitants such as carbonates, bicarbonates, hydroxides, etc. This “up-front” pre-treatment to remove the alkaline metal cations prior to the processing liquid being recovered invariably involves equipment such as residence tanks, valves, pumps, piping, filters, filter presses, and other equipment commonly used for separating precipitated solids from the processing liquid prior to regeneration and/or reclamation of the latter. In short, this pretreatment to remove the alkaline earth metal cations is expensive and can involve the utilization of valuable space, e.g., if the system was on an offshore platform.